Rubber goods such as tire treads often are made from elastomeric compositions that contain one or more reinforcing materials such as, for example, particulate carbon black and silica; see, e.g., The Vanderbilt Rubber Handbook, 13th ed. (1990), pp. 603-04.
Good traction and resistance to abrasion are primary considerations for tire treads; however, motor vehicle fuel efficiency concerns argue for a minimization in their rolling resistance, which correlates with a reduction in hysteresis and heat build-up during operation of the tire. These considerations are, to a great extent, competing and somewhat contradictory: treads made from compositions designed to provide good road traction usually exhibit increased rolling resistance and vice versa.
Filler(s), polymer(s), and additives typically are chosen so as to provide an acceptable compromise or balance of these properties. Ensuring that reinforcing filler(s) are well dispersed throughout the elastomeric material(s) both enhances processability and acts to improve physical properties. Dispersion of fillers can be improved by increasing their interaction with the elastomer(s). Examples of efforts of this type include high temperature mixing in the presence of selectively reactive promoters, surface oxidation of compounding materials, and surface grafting.
The section of a polymer chain from the site of the last crosslink to an end of the polymer chain is not tied to the macromolecular network and thus cannot be involved in an efficient elastic recovery process. As a result, energy transmitted to this section of the polymer (and vulcanizate in which such polymer is incorporated) is lost as heat, making such free ends a major source of hysteretic losses. Ensuring that polymer chain ends are tied to, or otherwise interact well with, reinforcing particulate fillers, is important to many vulcanizate physical properties such as, for example, reduced hysteresis. Chemically modifying the polymer, typically at a terminus thereof, is one of the most effective ways of increasing interactivity of fillers and polymers.
Various elastomeric materials are used in the manufacture of vulcanizates, including tire components. In addition to natural rubber, some of the most commonly employed include high-cis polybutadiene, often made by processes employing catalysts, and substantially random styrene/butadiene interpolymers, often made by processes employing anionic initiators. A reactant that can provide a terminal functional group to a carbanionic (anionically initiated) styrene/butadiene interpolymer often will not react with the pseudo-living end of high-cis polybutadiene and, to a lesser extent, vice versa.
Attachment of certain functional groups, including hydroxyl groups, thiol groups, primary and secondary amine groups, and phosphine groups, to terminally active polymers, particularly carbanionic polymers, is difficult. The active hydrogen atoms present in such groups tends to quench or terminate the terminally active polymer. This undesired termination some-times can be avoided through use of indirect attachment schemes, i.e., reaction schemes that allow for attachment of compounds that contain other types of functional groups which then can be converted to the desired active hydrogen atom-containing functional group.